A recent 451 Group report notes that venture capital investments in open source companies are at an all time high this quarter. http://blogs.the451group.com/opensource/2008/04/01/vc-funding-for-open-source-hits-an-all-time-high/. They raised $203.75m, up from $100.40m in the same quarter of 2007. He expresses caution that few of the deals were seed or Series A and that much of the funding was raised by some mature companies, such as SugarCRM.
This increase in funding for open source experience is consistant with what I am seeing in Silicon Valley where I work with about 40 startups (not all open source). Most software venture deals have an open source component to them and venture capitalists are very interested in new open source projects. I know of at least four new open source companies that are seeking funding, several are based on existing projects. So I disagree with Matt that the relatively smaller number of seed and Series A deals are a cause for concern. Seed deals in particular are difficult to find (several of the companies that I mentioned above have bootstrapped or used friends and family money, so they are basically invisible). In addition, I know of four foreign open source companies that are coming to the US because of the size of the market and the depth of the venture capital market. I think that 2008 will be another record year for open source funding.